Pediatric emergency medicine trisk 1164

after each application The shunt tap is performed by inserting a 23- or 25-gauge butterfly obliquely into the reservoir and holding the butterfly tubing perpendicular to the floor The height of the CSF rise into the butterfly tubing, measured in centimeters, is the ICP Normal pressure is between and 10 cm H2 O; pressure of more than 20 cm H2 O is indicative of distal shunt malfunction requiring urgent revision Slow or absent flow from the proximal reservoir (especially with occlusion of the distal reservoir of a double-reservoir shunt) is highly predictive of proximal shunt obstruction In this case, the physician may notice that the reservoir collapses when gentle suction is applied to the butterfly with a syringe It is important to avoid further suctioning of this reservoir because this could lead to aspiration of debris into the proximal catheter, causing a blockage where one did not previously exist Poor flow during the shunt tap can also indicate noncommunicating hydrocephalus, which may be diagnosed by imaging studies and lumbar puncture The shunt tap can be therapeutic and diagnostic The child with a distal shunt obstruction or partial proximal obstruction may be eligible for urgent, rather than emergent, shunt revision if symptoms of increased ICP are alleviated after the tap However, removal of too much fluid should be avoided because abrupt fluid shifts within the cranial vault can lead to disruption of subdural vessels It is prudent to remove just enough fluid to decrease the ICP below 20 cm H2 O and repeat the procedure if symptoms return before definitive surgical management FIGURE 135.5 Burr-hole puncture The child with complete obstruction of the proximal catheter does not obtain relief of symptoms after a shunt tap because the obstruction prevents adequate aspiration of fluid from the ventricles These children usually respond temporarily to medical management that decreases their ICP; however, it should be stressed that restoration of shunt integrity and function is the permanent treatment of shunt obstruction In the emergent situation, this treatment includes the administration of 3% normal saline (5 mL/kg bolus) Further therapy is with acetazolamide (Diamox) 30 to 80 mg/kg/day and Decadron mg/kg/day and hyperventilation in the unstable patient The following procedures are not commonly performed in the ED, and even more rarely performed by a clinician other than a neurosurgeon If the child is experiencing life-threatening symptoms from proximal obstruction, is unable to undergo immediate surgical repair, and is unresponsive to medical management, a burr-hole puncture procedure may be performed ( Fig 135.5 ) This should be performed only in dire circumstances, as the procedure carries with it lifethreatening risks such as disruption of intraparenchymal vessels and tissue By nature of the procedure itself, the proximal shunt catheter is torn and urgent revision is therefore mandatory The burr hole is best identified by direct palpation and confirmation with the skull radiographs For example, some reservoirs are not always located over the burr hole A 3½-in spinal needle is inserted perpendicular to the skull through the burr hole to a depth of no more than cm H2 O After the stylet is removed, fluid should drain spontaneously and should be allowed to so until flow slows down The patient’s condition should stabilize sufficiently for transport to an operating suite or tertiary care institution Another method of temporarily relieving a lumen obstruction is to flush a small amount of sterile saline through the clogged tubing in an attempt to dislodge the obstruction This method can be used for distal or proximal obstructions, with the caveat that instilling a few more milliliters into the ventricles may in fact worsen the patient’s condition If this procedure is performed with a double-bubble device, the reservoir that is not being used must be compressed to allow the fluid to go in only one direction In an infant with an open fontanel, the physician can aspirate fluid through a direct ventricular puncture ( Fig 135.6 ) This procedure also carries a significant risk of parenchymal injury should be performed only when prompt surgery is impossible FIGURE 135.6 Ventricular tap through open fontanel Infection The reported incidence of CSF shunt infections ranges between 5% and 10% and depends on the center performing the study and the criteria used to define infection The majority of infections are perioperative in nature Recent advances have reduced the rate of infection, including allowing fewer operating room personnel, soaking the shunt in antibiotics before insertion, and administering prophylactic antibiotics Infections generally occur within months of shunt placement, with a higher incidence of infections in children younger than years Other risk factors include insertion of the shunt into a premature infant and insertion after a previous infection The common organisms cultured from infected CSF shunts are gram-positive bacteria ( Table 135.3 ) Staphylococci adhere well to Silastic tubing, and these infections are often difficult to eradicate without removal of the catheter Infections with S epidermidis , S aureus , and P acnes are common within the first few weeks after surgery Infections that occur more than months after shunt placement are more likely due to gram-negative infections caused by H influenzae infection, bowel erosion, or pressure necrosis from the shunt apparatus Fungi are rare pathogens occasionally seen in premature infants External infection of skin and subcutaneous tissue overlying the shunt hardware can occur; however, these superficial infections may not lead to shunt infection if treated promptly Necrosis of the area around the reservoir can occur as a result of the constant pressure in infants or nonambulatory patients Skin breakdown leading to visualization of the shunt mechanism is, by definition, a shunt infection and must be treated accordingly TABLE 135.3 COMMON ORGANISMS INVOLVED IN CEREBROSPINAL FLUID SHUNT INFECTIONS Gram positive Gram negative Coagulase-negative Escherichia coli staphylococci (Staphylococcus epidermidis ) Staphylococcus aureus Enterococcus species Streptococcus species Haemophilus influenzae